Electric motor protective system



23, 1545. CFEQSMAN z ssmrfi ELECTRIC MOTOR PROTECTIVE SYSTEM 1 Filed June 3, 1943 i L /NE Sill/TC INVENTOR ZOE/N6 P Clears/MN.

ATTORNEY Patented Oct. 23, 1945 ELECTRIC MOTOR PRUIECTIVE SYSTEM Luring Pickering Crosman, South Orange, i i. 1., assignor to Monroe Calculating Machine Company, Orange, N. J., a corporation of Delaware Application June 3, 1943, Serial No. 489,522

6 Claims.

The invention relates to motor protective systems for electric drive calculators, as well as for other machines and devices. In such protective systems, it is desirable to provide means including a thermal responsive circuit controlling device or safety switch adapted to protect the motor against abnormally high temperatures in stalled conditions. These stalled conditions are not likely to occur during starting and acceleration of the speed of the motor to normal, during which time the load is comparatively light, notwithstanding more power is needed, but rather during operation of the machine in the performance of arithmetical problems when the motor may become subjected to overload for short periods of time. It is not desirable to break the motor circuit on this account and it is an object of the invention to provide means including a thermal responsive circuit controlling device or safety switch adapted to break the motor circuit should the motor become stalled in such cases. Another object is to provide such means'adapted to govern the speed of the motor. Other objects and advantages will appear hereinafter, or will be obvious.

, The invention consists in the novel construction and combinations of parts as hereinafter set forth in the claims.

In the accompanying drawing the figure is a diagrammatic view of the invention, with parts thereof in section.

In the drawing, the numeral I designates the customary electric outlet plug, and 2 is the line switch, operable to throw the motor 3 into and out of operation, subject to the invention or controls now to be described.

A centrifugal circuit controlling device or governor includes a spring urged governor lever 4, fulcrummed at 5 to an insulation block 6, made fast to the motor shaft 1 by a set screw 8.

Upon throwing the line switch 2, the current will flow from the plus terminal of the plug through'a Spencer thermostatic switch or thermal responsive circuit controlling device 9, of known commercial design to binding post Ill mounted upon an insulation block H; to leaf spring [2 securedto insulation block H by said binding post; to plate lever l3 fulcrumed at 13' within a slot of a bracket l4 also secured to said insulation block I I by said binding post, said plate lever being held against the outer edge wall of said slot by said leaf spring the free end of which also engages said slot; to the spring-urged lever 4 of the centrifugal governor; to the coiled spring l5 urging said lever, which spring is superior to leaf spring 12; to the collector ring 15 of said governor, which ring is wiped by brush ii in the rotation of. said motor and is made fast to the insulation block 6 by a screw or screws lB en gaging a perforation of clamp ring 19; and through the primary coils of the motor to the other terminal of said outlet plug.

The free end of one arm of said governor lever 4 has contact normally at 20 through the urge of the coiled spring of said lever and that of leai spring 12, with a screw 2| adiustably engaging a threaded aperture of the free end of one arm of said plate lever. A screw ll mounted upon insulation block H and adjustably engaging a threaded aperture of said bracket l4, contacts the leaf spring 12 intermediately of the length of the latter to stiffen said leaf spring and hold it to its work.

A condenser 22 is normally located in a shunt 23, 23' across the brush of the motor and said centrifugal governor. A resistance coil or resistor 24 is connected in said shunt across the condenser and serves as a by-pass through which a. proportion of the current to the condenser may flow around the same.

The motor being started, upon acceleration of the speed thereof to normal the centrifugal governor lever 4 will be actuated against the tension of its coiled spring l5, thereby retracting its contact arm 20 relative to the contact screw 2| and permitting the plate lever l3 urged by its leaf spring I2 to make contact at the free end of the other or shorter arm of said plate lever at 25 with a binding post 26 mounted upon said insulation block II and wired at 21 to the wire 28 connecting the plus terminal of the outlet plug with one of the contacts of the thermostatic switch 9, the parts 20, 2| being meanwhile retained in contact due to the urge of the leaf spring [2; and inasmuch as the other contact of the thermostatic switch 9 is wired at 9 to the binding post Ill as aforesaid, the result will be the shunting of the thermostatic switch 9 and flow of the current through the plate lever l3 to the motor. Wiring 9' is also connected with one end of the shunt 23, 23 wherein the condenser and resistor are located.

In the event that the motor should race or have the speed thereof further accelerated sub stantially above normal, the spring-urged lever 4 of the centrifugal governor will be further "actuated to thereb break the contact of the parts 20, 2|, the parts 25, 26 being meanwhile retained in contact due to the urge of the leaf spring l2 so that the current will now flow through the plate lever l3, leaf spring [2 and binding post it! to the condenser 22 and resistor 24 and there from to the motor, said condenser and resistor being thus brought in series circuit with the motor, the resistor functioning to reduce the potential or electro-motive force of the current and tending to reduce the speed'of the motor to.

motor and the condenser and resistor are located in a shunt of said circuit; and inasmuch as the work previously performed by the current in operating the motor will be transformed'into heat, the thermostatic switch 9 will function to break the motor circuit.

It Will be obvious that in substitution for the thermostatic switch some other form of circuit maker and breaker responsive to heat generated by'the current in the electric circuit may be used such as those devices known as fuses.

. I claim:

1. In an electric motor protective system, means for starting the motor, accelerating the speed thereof to normal and retaining themotor in operation notwithstanding subjection thereof to overload for short periods of time and for breaking the circuit. should the motor become stalled, including a thermal responsive circuit controlling device, and a centrifugal circuit controlling device, both devices being in series circuit with the motor, said centrifugal circuit controlling device including means for causing said thermal responsive device should the motor become stalled.

2. In an. electric motor protective system, means for starting the motor, accelerating the speed thereof tonormal and retaining the motor in operation, notwithstanding subjection thereof to overload for. short periods of time, for governing the speed of the motor and for breaking the circuit should the motor become stalled, including a thermal responsive circuit controlling device and a centrifugal circuit controlling device, both devices being in series circuit with the motor, and a condenser and a resistor located in a shunt of said centrifugal circuit controlling device, said centrifugal device including means for causing said thermal responsive device to be shunted upon acceleration of the speed of the motor to normal, for switching said condenser and resistor into series circuit with the motor upon further acceleration of the speed of the motor substantially above normal and for restoring said thermal responsive device into series circuit with the motor and thereby permitting-the motor circuit to be broken by the thermaLresponsive device should the motor become stalled.

3. In an electric motor protective system, a motor, a source of power, means including a line switch for connecting the motor to the source of power to establish a motor circuit, a thermal responsive circuit controlling device in the motor circuit, and a centrifugal circuit controlling device including means to cause said thermal responsive device to be shunted upon acceleration of the speed of the motor to normal and to restore said thermal responsive device in series circuit with the motor and thereby permit the motor circuit to be broken by said thermal responsive device should the motor become stalled.

4. In an electric motor protective system, a motor, a source of power, means including a line switch for connecting said motor to the source of power to establish a motor circuit, a thermal respnsive circuit controlling device in the motor circuit, a centrifugal circuit controlling device and a condenser and a resistor located in a shunt of said centrifugal circuit controlling device, said centrifugal device including means to cause said thermal responsive device to be shunted upon acceleration of the speed of the motor to normal, to switch said condenser and resistor into series circuit with the motor upon further acceleration of the speed of the motor substantially above normal, and to restore said thermal responsive 7,

device into series circuit with the motor and thereby permit the motor circuit to be broken by said thermal responsive device should the motor become stalled.

5. In an electric motor protective System, means for starting the motor, accelerating the speed thereof to normal and retaining the motor in operation notwithstanding subjection thereof to overload for short periods of time and for breaking the motor circuit should the motor become stalled, including a, thermal responsive circuit controlling device, and a centrifugal circuit controlling device, both devices being in series circuit with the motor, said centrifugal circuit controlling device including means having two spring-urged elements the spring of one of which is superior to that of the other for causing said thermal responsive device to be shunted upon acceleration of the speed of the motor to normal and for restoring said thermal responsive device into series circuit with the motor and thereby permitting the motor circuit to be broken by said thermal responsive device should the motor .be-

' come stalled.

6. In an electric motor protective system, a motor, a source of power, means including a line switch for connecting said motor to the source of power to establish a motor circuit, a thermal responsive circuit controlling device in the motor circuit, and a centrifugal circuit controlling device including means having two spring-urged elements the spring of one of which is superior to that of the other to cause said thermal responsive device to be shunted upon acceleration of the speed of the motor to normal and to restore said thermal responsive device into series circuit with the motor and thereby permit the motor circuit to be broken by said thermal responsive device should the motor become stalled.

LORING PICKERING CROSMAN. 

